1. Technical Field
The present invention relates to a multipath signal reliability determination method, a code phase error calculation method, a code phase calculation method, a position calculation method, and a multipath signal reliability determination device.
2. Related Art
A GPS (Global Positioning System) is widely known as a positioning system using positioning signals and is built into mobile phones, car navigation systems, and the like. The GPS carries out positioning calculation processing to obtain the position of a position calculation device on the basis of information regarding the positions of a plurality of GPS satellites or the pseudo distance between the respective GPS satellites and the position calculation device.
Multipath is one of the main factors which cause errors in position calculation using positioning signals. An environment where multipath occurs is referred to as “multipath environment”. The multipath environment means an environment where indirect wave signals, such as waves reflected from buildings, the ground, or the like, transmission waves transmitted through obstacles, and diffraction waves diffracted by obstacles, are superimposed on direct wave signals transmitted from a signal generation source of the positioning signals (in the case of GPS, GPS satellites), and are received as multipath signals. Under this environment, indirect waves appear as error signals, making it difficult to decode codes.
In order to solve the problems regarding the errors due to multipath, for example, JP-A-2008-170214 describes a technique to determine a positioning satellite that has a high probability of having multipath influence as an unsuitable positioning satellite, so to be able to calculate the position by excluding the unsuitable positioning satellite.
One way to deal with multipath is to calculate a position by excluding a multipath signal from acquired positioning signals. However, in an urban canyon environment where tall buildings are adjacent to each other, most of received positioning signals may be multipath signals, and if all the multipath signals are excluded, the number of satellites necessary for position calculation may not be secured. For this reason, there is a demand in position calculation to use positioning signals that are reliable enough for use in the position calculation, despite these signals may all be multipath signals.